1. Field of the Invention
The present invention relates generally to a power output mechanism for power tools, and more particularly, to a power output mechanism which switches gears smoothly.
2. Background Art
A conventional power tool includes an output shaft which rotates to output torque or impacts the object to provide a impact force to the object. A switch mechanism is provided to switch different gears of status for the output power, and generally the last gear provides rotation and impact simultaneously. However, the conventional power tool includes a complicated structure which includes a base part, a switch unit, an impact unit, a pressing unit, an output shaft and an operation member. The switch unit includes multiple positioning plates which are installed in a frame and the impact unit includes an orientation wheel movably connected to the output shaft and an operation wheel fixed to the output shaft. The orientation wheel and the operation wheel each have a toothed contact surface and the two toothed contact surfaces are engaged with each other. The orientation wheel and the operation wheel are engaged with each other on their corresponding toothed contact surfaces so that when rotating the operation member, the protrusions on the rotation collar driven by the operation member press on the positioning plates such that the positioning plates are engaged with the flanges defined on the outer periphery of the orientation wheel. The rotation of the orientation wheel is limited. In this situation, when the orientation wheel and the operation wheel are moved relative to each other, the operation wheel jumps relative to the orientation wheel due to the toothed contact surfaces. The movement of the operation wheel provides the output shaft an intermittent impact to the object.
However, when the operation member is rotated to an impact position, the positioning plates may fail to insert into the gaps between the flanges of the orientation wheel and engage with flanges to limit the rotation of the orientation wheel. The user has to re-operate again or even more times to set the power tool to the impact mode.